Optical reproduction apparatus

ABSTRACT

The object of the present invention is to provide an optical disc, a method of manufacturing thereof and an optical reproduction apparatus including the same wherein defects and deterioration in the optical disc are minimized at the time of manufacture, during operation and storage thereof as well. The invention conceives an optical disc suitable for accomplishing the above object through specifications such as providing a cross-sectional structure thereof comprising a pair of transparent substrates each provided with at least one layer of a recording film formed on the surface of information patterns thereof, with the pair being bonded and laminated with an adhesive, and further providing an instantaneous axial acceleration &lt;2G measured at room temperatures, a skew angle &lt;5 mrad measured at room temperatures, and a skew angle &lt;5 mrad measured after being left for one hour as heated to 80° C. (otherwise, a shear mass &lt;20 μm measured after being left for one hour as heated to 80° C.), and still further by utilizing a reaction adhesive the hardness of which after cure is between A30 and A80 in Shore hardness. On the other hand, preferred methods of manufacturing optical discs suitable for implementing the object of the invention were set forth, which utilize reaction adhesives having a Shore hardness after cure between A30 and A80.

This is a continuation of application Ser. No. 08/375,730, filed Jan.20, 1995, now U.S. Pat. No. 5,543,271, which is a continuationapplication of application Ser. No. 08/053,483, filed Apr. 29, 1993 (nowU.S. Pat. No. 5,401,610) which is a divisional application ofapplication Ser. No. 07/855,511, filed Mar. 20, 1992 (now U.S. Pat. No.5,244,775).

BACKGROUND OF THE INVENTION

The present invention relates to an optical disc suitable for use inpreservation, recording and reproduction of audio signals, images,information and the like, and also to a method of its manufacture.

The optical discs are generally composed of a pair of recording metallaminae each having grooves or pits shaped irregularities for servotracking or the like, formed on a glass, transparent plastic or the liketransparent replica substrate, with the same metal laminae disposed at acertain distance facing each other and bonded together with adhesive.Recently, increasing demands for such optical discs to increase theamount of information to be stored, to speed up the processing speed orthe like are becoming greater at a rapid pace. In order to satisfy suchdemands, it is necessary to increase memory capacity and to rotate theoptical discs at a higher speed.

Thereby, in lamination bonding of the substrates as processed as abovein prior art optical discs, the following adhesives are used because ofthe simplicity, reduced-cost and the like in their manufacture. (1)thermoplastic hot-melt adhesives, (2) one-part anaerobic adhesives asdisclosed in Japanese Patent Publication Laid-Open No.61-151853, whichwas a reactive adhesive utilized to suppress disc deformation, and (3)two-part unmixture adhesives as disclosed in Japanese Patent PublicationNo. 61-50231.

These methods, however, involve the following problems, respectively.That is, (1) the thermoplastic hot-melt adhesive is inevitablyaccompanied with at least one of the defects resulting from heat whenapplying the adhesive or from pressure when lamination bonding, plasticor elastic deformation during a high speed operation, and warp orpeeling due to aging during storage. Further with respect to thereactive adhesive, (2) the one-part anaerobic adhesive, as it cures in asecond order and is bonded and laminated under normal pressures, allowsair bubbles to form readily therein which are difficult to evacuate onceincluded, thereby the same is cured with the air bubbles as includedinto a hard body which is too hard to absorb the air bubbles as much assufficiently to relax them, thereby resulting in a poor flatness of thesurface of the disc, or causing defects due to corrosion in therecording layer or medium due to uncured parts in the air bubbles. (3)The two-part unmixture adhesive is applied separately of the two-partsto a thickness of several tens μm, respectively, then bonded together.At that time, as thus applied films are provided in a thick liquid form,there occurs a flow of the adhesive in the interface of laminationbonding due to the pressure applied at the time of lamination bonding,thereby causing uneven mixing thereof, thus, uneven curing, and furtherbecause of the hardness of the cured body, there occur wrinkles in therecording layer or medium, which becomes a cause of a poor performancein recording and reproduction.

As explained hereinabove, the prior art method (1) has the problem thatthere occur defects at least at the time of manufacture, at the time ofutilization or at the time of storage of the optical discs. Further,with respect to the prior art methods (2) and (3), there arises aproblem at the time of manufacture of the optical discs.

OBJECT AND SUMMARY OF THE INVENTION

The main object of the present invention is to solve the foregoingproblems in the prior art, and to provide an optical reproductionapparatus including an optical head and an optical disc in which thedefects at the time of manufacture thereof, deformation due to highspeed access or high speed rotation during its operation, and warp orpeeling due to aging during storage of the optical disc are minimized,and also a method of its manufacture.

This object of the invention with respect to the optical disc, iscapable of being accomplished by providing at least one of the followingmeans from (A) to (C).

(A) An optical reproduction apparatus including an optical head and anoptical disc having a cross-sectional structure comprising a pair oftransparent substrates, each having at least one layer of a recordingfilm formed on its surface having information patterns, and each bondedtogether with adhesive, wherein the same is characterized by having aninstantaneous axial acceleration <2 G measured at room temperatures, askew angle <5 mrad measured at room temperatures, and a skew angle <5mrad measured at room temperatures after being left for one hour asheated at 80° C.

(B) An optical reproduction apparatus including an optical head and anoptical disc having a cross-sectional structure comprising a pair oftransparent substrates, each having at least one layer of a recordingfilm formed on its surface having information patterns, and each bondedtogether with adhesive, wherein the same is characterized by having aninstantaneous axial acceleration <2 G measured at room temperatures, askew angle <5 mrad measured at room temperatures, and a shear mass <20μm measured at room temperatures after being left for one hour as heatedat 80° C.

(C) An optical reproduction apparatus including an optical head and anoptical disc having a cross-sectional structure comprising a pair oftransparent substrates, each having at least one layer of a recordingfilm formed on its surface having information patterns, and each bondedtogether with adhesive, wherein said adhesive is characterized by beinga reactive type adhesive which has a Shore hardness between A30 and A80after cure.

Further, the methods of manufacturing such optical discs reproductionapparatus as above can be accomplished by providing at least one of thefollowing processes from (D) through (F) for manufacturing the opticaldisc thereof.

(D) A method of manufacturing optical discs characterized by comprisingsteps of:

(1) forming a ultraviolet (UV) curing resin on the surface of a stamperwhich has information patterns, and forming a transparent substrate oversaid UV curing resin,

(2) irradiating ultraviolet rays for exposure, and transferring theinformation patterns from the surface of the stamper to the UV curedresin and the transparent substrate,

(3) removing or severing the UV cured resin and the transparentsubstrate from the surface of the stamper having the informationpatterns, and obtaining a replica substrate thereof,

(4) forming a recording film (lamina) on the surface of the replicasubstrate having duplicated information patterns, and

(5) disposing a pair of replica substrates each provided with arecording film such that the sides of the recording films face eachother, and bonding and laminating the pair with reactive adhesive whichhas a Shore hardness between A30 and A80 after cure.

(E) A method of manufacturing optical discs characterized by comprisingsteps of:

(1) forming a transparent substrate on the surface of a stamper havinginformation patterns, and transferring the information patterns from thestamper to the transparent substrate,

(2) severing the transparent substrate off from the surface of thestamper having information patterns, and obtaining a replica substrate,

(3) forming a recording film on the surface of the replica substratehaving information patterns, and

(4) disposing a pair of replica substrates each provided with arecording film such that the sides of the recording films face eachother, and bonding and laminating the pair with reactive adhesive whichhas a Shore hardness between A30 and A80 after cure.

(F) A method of manufacturing optical discs characterized by comprisingsteps of forming a recording film on the surface of the replicasubstrate having information patterns, disposing a pair of replicasubstrates each provided with a recording film such that the sides ofthe recording films face each other, and bonding and laminating the pairwith reactive adhesive which has a Shore hardness between A30 and A80after cure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exterior view of an optical disc.

FIG. 2 shows a cross-sectional view of an optical disc.

FIG. 3 shows process diagrams explanatory of manufacturing processes ofa stamper.

FIG. 4 shows process diagrams explanatory of manufacturing processes ofan optical disc.

FIG. 5 shows another process diagram explanatory of manufacturingprocesses of an optical disc.

FIG. 6 shows still another process diagram explanatory of manufacturingprocesses of an optical disc.

FIG. 7 shows still further process diagram explanatory of manufacturingprocesses of an optical disc.

FIG. 8 shows relationships between skew angles and adhesive hardness andalso between axial accelerations and the adhesive hardness.

FIG. 9 shows reaction adhesive compositions.

FIG. 10 shows reaction adhesive compositions.

FIG. 11 shows adhesive compositions.

FIG. 12 shows properties of optical discs.

FIG. 13 shows properties of optical discs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The inventors of the present invention have discussed preferredspecifications for the optical disc from a view point of minimizing thedefects in the optical disc arising at the time of its manufacture,deformation due to high speed access and high speed rotation during itsoperation, and warp and deflection or peeling due to aging understorage.

As a result, the inventors have gained considerable knowledge as followson the optimization of the design specifications for the optical disc.(A) The object of the present invention is capable of being accomplishedby providing an optical disc having a cross-sectional structurecomprising a pair of transparent substrates, each provided with at leastone layer of a recording film formed on the plane of informationpatterns thereof, and bonding and laminating the pair with an adhesive,wherein the same optical disc is characterized by having aninstantaneous axial acceleration <2 G measured at room temperatures, askew angle <5 mrad measured at room temperatures, and a skew angle <5mrad measured at room temperatures after being left for one hour asheated at 80° C. The last part of the above expression that "a skewangle <5 mrad measured at room temperatures, and a skew angle <5 mradmeasured at room temperatures after being left for one hour as heated at80° C." can be rewritten in terms of shear mass such that "a shear mass<20 μm measured at room temperatures after being left for one hour asheated at 80° C." An optical disc which satisfies the designspecifications of the invention is free from defects arising from at thetime of manufacture, deformation due to high speed access or high speedrotation during its operation, and warp and deflection or peeling due toaging under storage. The design specifications according to the presentinvention will be set forth in the following.

The foregoing instantaneous axial acceleration refers to aninstantaneous axial acceleration exerted upon the plane of the opticaldisc during its rotation, corresponding to the degree of irregularitydefects in the surface of an optical disc. Thereby, the greater theaxial acceleration measured, the greater the irregularity defects arepresent, which, thereby provides information on the existence or thedegree of defects arising at the time of its manufacture. The skew anglerefers to an angle of deflection between the incident laser beams andthe reflecting beams thereof. As the greater skew angle measuredindicates the greater degrees of the deformation, warps or peeling beingpresent, thereby it will be possible to obtain information regardingdeformation due to high speed access or high speed rotation duringoperation of the optical disc, and warp or peeling due to aging duringits storage. The shear mass refers to a shear occurring between a pairof transparent substrates each having at least one layer of a recordingfilm formed on the plane of information patterns. As the greater shearmass indicates there being present a greater degree of deformation orpeeling, it thereby enables to provide information on the deformationdue to high speed access or high speed rotation during operation of theoptical disc, and also warps or peeling due to aging during its storage.Thereby, with respect to the deformation or peeling in the optical disc,pertinent information can be obtained through at least one of the skewangle and the shear mass measured.

Further, the instantaneous axial acceleration, the skew angle and theshear mass will be described quantitatively in the following. Thequantities of these parameters as above are determined as to whetherthey can provide an optical disc, given with such quantities, capable ofrecording and reproducing information, and also as to whether thedefects, deformation and peeling can be detected through visualinspection.

In a recording head for writing and reproducing information with laserbeams on or from an optical disc, laser beams are focused on the planeof the optical disc through a condensing lens in the head to write orread information for storage or reproduction. However, due to anydefects, deformation or peeling in the optical disc, in case the laserbeams become impossible to be focused, inadequate recording andreproduction properties result in. Thereby, there exists a closerelationship between the properties of the optical disc and that of theoptical head, thus, judgement regarding the properties of any opticaldisc whether it is excellent or inferior must be done in fullconsideration also of the properties of a related optical head. Thereby,according to the present invention, an optical head having a focus depthof about 2 micron meter indicative of its typical optical properties hasbeen utilized in experiments to verify its applicability in recordingand reproducing information under various conditions. As the result ofexperiments, it has been concluded that an optical disc having aninstantaneous axial acceleration <2 G measured at room temperatures, askew angle <5 mrad measured at room temperatures, a skew angle <5 mradmeasured at room temperatures after being left for one hour as heated at80° C., and a shear mass <20 μm measured at room temperatures afterbeing left for one hour as heated at 80° C. is capable of recording andreproducing information effectively. Further, the focusing depth isgiven by λ/(NA)², where NA is the number of aperture of a lens, and λ isthe wavelength of a laser beam source. On the other hand, with respectto the visual inspection, existence of any defects, deformation orpeeling in the optical discs has been checked through irradiating thesurface of an optical disc with light, and projecting its reflectivelight to form a magnified image for easier inspection. Further, themeasurements on the instantaneous axial acceleration, the skew anglesand the shear mass have been conducted at room temperatures. As for theskew angles and shear mass, however, they were measured both at roomtemperatures and after being left for one hour as heated to 80° C.Namely, the measurements of the instantaneous axial acceleration havebeen conducted only at room temperatures, as they are sufficient toprovide information on the defects arising at the time of manufacture ofthe optical discs. However, the measurements of the skew angles andshear mass have been conducted also after leaving the optical discs forone hour as heated to 80° C., in consideration that the heat generatedin an optical disc system subject to high speed access or high speedrotation during operation thereof, or the temperature thereof understorage may become 50° C. or so. According to the present invention, inorder to make appraisal thereof in a short time, the measurements on theoptical disc have been carried out after being left for one hour asheated to 80° C., which approximately corresponds to a case where thesame is left for 1000 hours at temperatures between 50° and 60° C. Bymeans of such arrangements and procedures, pertinent informationregarding deformation due to high speed access or high speed rotationduring operation of the optical disc, and warps and deflection orpeeling in the optical disc due to aging under storage thereof can beobtained. Examples of the experiments conducted on respective cases willbe described in detail later. Then, from the results of suchexperiments, the aforementioned object of the present invention has beenverified to be accomplished according to the design specifications forthe optical disc pursuant to the present invention. Concurrently,another knowledge as to preferred adhesives has been obtained such thatin order to satisfy the object of the present invention an adhesive tobe utilized should be reaction type adhesive and should have a Shorehardness between A30 and A80 after cure.

This knowledge obtained on the preferred adhesives will be described indetail in the following. In order to prevent the inclusion of defects atthe time of manufacture of optical discs, the design specifications forthe optical discs may only satisfy such that the instantaneous axialacceleration be less than 2 G. As the result of the experimentsconducted taking special notice on the preferred adhesives to beemployed, it has been concluded that such adhesives should be limited tothe reaction adhesives and its Shore hardness value should be less thanA80. On the other hand, in order to preclude dynamic deformation due tohigh speed access or high speed rotation during operation of opticaldiscs, and warps and deflection or peeling due to aging thereof understorage, the design specifications for the preferred optical discsshould be adapted only to satisfy such that the skew angle measured atroom temperatures be less than 5 mrad., and that the skew angle measuredafter being left for one hour as heated to 80° C. be less than 5 mrad.As the result of the experiments conducted taking special notice of thepreferable adhesives to be employed, it has been concluded that suchadhesives should be limited to the reaction adhesive and its Shorehardness value should be greater than A30. Further, the foregoingexpression that "the skew angle measured after being left for one houras heated to 80° C. be less than 5 mrad" may be restated in terms of theshear mass such that "the shear mass measured after being left for onehour as heated up to 80° C. be less than 20 μm". Thereby, as the result,it has been concluded that in order to preclude defects in the opticaldiscs at the time of manufacture thereof, dynamic deformation due tohigh speed access or high speed rotation during operation thereof, andwarps and deflection or peeling due to aging during storage thereof, itis preferred for the adhesives to be a reaction type and to have a Shorehardness between A30 and A80 after cure.

Next, preferred methods of manufacturing optical discs havingaforementioned design specifications will be set forth from (D) through(F) below.

(D) A method of manufacturing optical discs characterized by comprisingsteps of:

(1) forming a UV curing resin on the surface of a stamper havinginformation patterns, and forming a transparent substrate on said UVcuring resin,

(2) irradiating Uv rays for exposure, and transferring the informationpatterns of the stamper to the UV curing resin and the transparentsubstrate,

(3) removing the UV cured resin and the transparent substrate from thesurface of the stamper having the information patterns to obtain areplica substrate,

(4) forming a recording film on the surface of the replica substratehaving information patterns, and

(5) disposing a pair of replica substrates each having a recording filmto face each other on the sides of the recording films, and bonding thepair with an adhesive which has a Shore hardness between A30 and A80.

(E) A method of manufacturing optical discs characterized by comprisingsteps of:

(1) forming a transparent substrate on the surface of a stamper havinginformation patterns, and transferring the information patterns of thestamper to the transparent substrate,

(2) severing the transparent substrate from the stamper, which wasformed on the surface of having its information patterns, and obtaininga replica substrate,

(3) forming a recording film on the surface of the replica substratehaving transferred information patterns, and

(4) disposing a pair of replica substrates each having a recording filmto face each other on the sides of the recording films, and bonding thepair with an adhesive which has a Shore hardness between A30 and A80.

(F) A method of manufacturing optical discs characterized by comprisingsteps of forming a recording film on the surface of the replica havinginformation patterns, disposing a pair of replica substrates having therecording film to face each other on the sides of the recording films,and bonding the pair with an adhesive which has a Shore hardness betweenA30 and A80.

In the following, the methods of manufacturing optical discs accordingto the present invention will be disclosed in detail. The stamperaccording to the present invention, the surface of which is formed suchas to have irregularities of recessed and raised portions correspondingto information patterns, is not specifically limited in the type or kindonly if its duplication mold is provided with a good releasability. Forinstance, it may include electro-cast stampers, resin mold stampers,glass stampers and the like.

The transparent substrate, which is a medium through which passes alaser beam for recording and reproducing information, is not limited inthe type or kind only if its optical distortion, a yardstick indicativeof its overall optical properties, is less than 50 nm. For example, suchwill include, without limiting thereof, substrates made of glass,polymethyl methacrylate, polycarbonate, polyolefine, thermal or lightcuring resins, and the like.

The recording film, which senses a light spot having a diameterapproximately between 0.6 and 1 μm, and forms record domains withoutgoing through phase changes or shape changes normal with such typessubjected to light or magnetic fields, is not limited in the kind ofmaterials only if it is provided with a C/N ratio larger than 60 dB. Forinstance, such will include, without limiting thereof, films made oftellurium oxides (TeOx), SbSe/BiTe lamination, rare earch transitionmetal amorphous alloys, TbFeCo oxides, GdTbFe oxides, DyFeCo oxides,TbDyFeCo oxides, garnet oxides, Pt/Co lamination, GeSbTe, InSeTeCo,InSbTe, In-Sb alloys and the like.

When a reaction adhesive selected consists of an accelerator primer anda one-part anaerobic adhesive, the lamination bonding process thereofwill become easier by separately applying the accelerator primercomponent to the surface of a recording film formed on the transparentsubstrate of one member of a pair to be laminated, and applying theone-part anaerobic adhesive component on the surface of a recording filmformed on the transparent substrate of another member of the pair to belaminated.

Lamination bonding under deoxygenation atmosphere permits a uniformreaction curing to proceed in the reaction adhesive thus preventing theoccurrence of uncured portions thereof. This is because that in thepresence of oxygen, radicals in the process of curing reactions reacteasily with oxygen, blocking uniform curing thereof, thereby adverselyaffecting to produce uncured portions thereof. Further, as long as thelamination bonding proceeds under deoxygenation atmosphere, there mayoccur no adverse effect, even if there are present nitrogen, inert gasesand the like.

Next, preferred reaction type adhesives utilized in manufacture ofoptical discs according to the present invention will be described indetail in the following. The reaction adhesive which bonds chemicallywith an object to be bonded through chemical reactions is superior tothe thermoplastic hot-melt adhesive in bonding strength, heat resistanceand mechanical strength. When applied to the manufacture of opticaldiscs, they are capable of providing high quality optical discs whichare highly reliable because of their excellent bonding strength, are fitfor use in various environments because of their excellent heatresistance, and withstand high speed rotation because of their excellentmechanical strength. In an example of experiments which will bedescribed in the following, a one-part anaerobic adhesive which uses anaccelerator primer in combination is utilized. The accelerator primerwhich serves to initiate curing reactions in the one-part anaerobicadhesive, is not limited in types or kinds, only if the curing processis not substantially affected by its amount to be applied. For instance,such will include, without limiting thereof, organometallic compounds,ferric chloride, ferrocene, cobalt naphthenic acid, and the like.Further, in order readily to provide a thin coating of the acceleratorprimer and concurrently to prevent the occurrence of any wrinkle due touneven curing, it is preferred for the viscosity thereof to be between 1and 100 cp. Further, a thickness of applied coating of the acceleratorprimer is preferably from 0.01 to 1 μm such as to ensure sufficientaction to be effected to initiate the reactions but to prevent a flow ofthe primer to occur during lamination bonding. The methods of applyingsuch accelerator primers are not limited only if they are capable ofproviding a coating thickness of 0.01 to 1 μm. For example, such willinclude, without limiting thereof, the spray coating, spin coating, rollcoating, dip coating and the like.

The one-part anaerobic adhesive is not limited to any particular typeprovided that its curing rate does not change according to the materialof surfaces to be bonded, and a curing rate for it alone is preferablyslow, which, however, can be adjusted to increase corresponding to theprocess speed of manufacture through contact with the acceleratorprimer. More particularly, such an adhesive having properties to cure in1 to 2 hours by it alone and cure in 30 seconds to 2 minutes when incontact with an accelerator primer will facilitate alignment orpositioning of a pair of transparent substrates to be laminated withimproved workability. Further, the composition of one-part anaerobicadhesives is made of a preferred mixture of a polymethacrylic monomer(or oligomer) as a main component thereof, a curing agent, anaccelerator, a preservation stabilizer and the like. Here, thepolymethacrylic monomer (or oligomer) refers to at least one of themultifunctional monomers and the one functional monomers, either usedalone or in mixture of two or more of them. The preferredmultifunctional acrylic monomer, for example, includes acrylate withpolyhydric alcohol, methacrylate with polyhydric alcohol,trymethylolpropan tryacrylate, trymethylolpropan trymethacrylate,neopenthyl glycol diacrylate, neopenthyl glycol dimethacrylate, ethyleneglycol diacrylate, ethylene glycol dimethacrylate, diethylene glycoldiacrylate, diethylene glycol dimethacrylate, epoxy acrylate, epoxymethacrylate, urethane polyacrylate, urethane polymethacrylate, 1.6hexanedihol diacrylate, 1.6 hexandihol dimethacrylate, 1.10 decanediholdiacrylate, 1.10 decanedihol dimethacrylate, dipentaerythritolhexaacrylate, dipentaerythritol hexamethacrylate, and the like. Next,the one functional acrylic monomer, for example, includes hydroxyethylacrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate,hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutylmethacrylate, tetrahydroflufyl acrylate, tetrahydroflufyl methacrylate,cyclohexyl acrylate, cyclohexyl methacrylate, benzyl acrylate, benzylmethacrylate, methoxypolyethylene glycol acrylate, lauryl acrylate,lauryl methacrylate, stearyl acrylate, stearyl methacrylate, isoborneolacrylate, isoborneol methacrylate, phenoxyethyl acrylate, phenoxyethylmethacrylate, phenoxypolyethylene glycol acrylate, phenoxypolyethyleneglycol methacrylate, and the like. The aforementioned curing agentincludes, for example, t-butyl hydroperoxide, p-methane hydroperoxide,cumene hydroperoxide, diisopropylbenzen hydroperoxide, and the like. Theforegoing accelerator includes, for example, ethanol amine, diethanolamine, triethanol amine, N.N dimethyl aniline, benzen sulphanilamide,cyclohexyl amine, triethyl amine, butyl amine and the like. Theaforementioned preservation stabilizer includes, for example,benzoquinone, hydroquinone, and the like. Further, preferred amounts ofa thickener, a plasticizer and the like may be added thereto.

Further, the aforementioned one-part anaerobic adhesive may well includesuch ones that cure under UV irradiation, provided that they accompanyno defects or corrosion in the record films due to air bubbles includedduring lamination bonding. Into such a one-part anaerobic UV curingadhesive is added a preferred amount of a photo polymerization initiatorfrom 1 to 5 wt % within which range the same will be effective toaccelerate, without detriment to, the curing reaction in the maincomponent. Such a photo polymerization initiator is utilized singularlyor in mixture of two or more of them, which include, for example,benzyl, benzyl class such as methyl-o-benzoate, benzoin, benzoinethylether, benzoinispropyl ether, benzoin class such as benzoinisbutylether, benzophenone, benzophenone class such as 4-methoxybenzophenone,acetophenone, acetophenone class such as 2.2-diethoxyacetophenone,benzylmethyl, 1-4(ispropylphenyl)-2-hydroxy-2-methylpropanal-1-, and thelike.

Preferred embodiments according to the present invention will be setforth in detail in the following with reference to the accompanyingdrawings.

Preferred Embodiments 1, 2

FIG. 1 shows an exterior view of an optical disc. A cross-sectional viewof the optical disc of FIG. 1 taken along A-B is shown in FIG. 2. Withreference to FIG. 2, an optical disc of an embodiment of the presentinvention is composed of a pair of replica plates 3, each provided witha recording layer, and bonded together via an adhesive. layer 4 having aShore hardness of A30 to A80. Each of the replica plates 3 provided withthe recording film consists of a replica plate 1 and a recording layer2.

For the above adhesives having a Shore hardness of A30 to A80, varioustypes of adhesives were prepared by mixing component group a andcomponent group b with their constituting components varied, and used incombination with an accelerator primer(Loctite's Locic) as shown in FIG.9, in which the component group a is selectively comprised of threekinds of constituting components of: a mixture acrylic anaerobicadhesive which comprises a base monomer of propylene glycol diacrylate(molecular weight: approx. 200) 45 weight part, a dilution monomer of1,10 decanedihol diacrylate 25 weight part, an adhesion acceleratormonomer of hydroxybutyl methacrylate 30 weight part and a peroxide 2weight part; an acrylic anaerobic adhesive available in the market(Loctite's 601); and another acrylic anaerobic UV curing adhesive(Loctite's 326), and the component group b is comprised of acrylicmonomers.

In this embodiment, adhesives of examples 1 and 2 in FIG. 9 wereutilized in the manufacture of a stamper to yield optical discsaccording to the present invention as illustrated in FIG. 3 from steps(a) through (f).

With reference to FIG. 3, a stamper is prepared as follows.

In step (a) a glass disc 1 (outer diameter: 350 mm, inner diameter: 10mm, thickness: 10 mm) both surfaces of which were polished is provided.In step (b) on one of the polished surfaces of glass disc 1 is formed apositive type photoresist 2 by spin coating to a thickness of 0.14 μm,thus providing a glass disc 3 with a photo resist. Then, in step (c) arecording machine writes information signals with Ar laser(wavelength:458 nm) in the surface of the photo resist of glass disc 3,then, the photo resist surface is developed to form recessed and raisedportions of grooves and pits representing the information signals, thusfurnishing a glass master disc 4. In step (d) a Ni film 5 is formed onthe surface of photo resist of the glass master disc 4 by the vapordeposition method to a thickness of 40 nm. Then, in step (e) anelectrocast film 6 is formed to a thickness of 300 μm by theelectroplating method utilizing the Ni film 5 as an electrode.Subsequently, in step (f) the glass disc 1 is severed from between Nifilm 5 to furnish a Ni stamper 7.

Then, by means of the stamper 7 thus furnished, optical discs areproduced according to a method of manufacture thereof as illustrated inFIG. 4 from (g-1) through (n-1).

The above stamper 7 is fitted in a mold support 8 in step (g-1), then instep (h-1) hot-melt polycarbonate resin 10 (molecular weight: approx.15000) is injected into a space 9 (outer dia.:300 mm, center poredia.:35 mm, thickness: 1.2 mm) inside the mold support to produce areplica substrate 11(outer dia.:300 mm, center pore dia.:35 mm,thickness: 1.2 mm) on the surface of which are transferred the recessedand raised portions of grooves and pits of the stamper as shown in step(i-1). Then, in step (j-1), on the surface of the replica substrate 11having information patterns thus duplicated, are formed a SiN enhancefilm 12 (30 nm thick), a TbFeCo magnetic film 13 (30 nm thick), an Alnreflective film 13 (30 nm thick), and a SiN protective film 14 (30 nmthick), layer on layer by sputtering, thereby furnishing a replicasubstrate 17 provided with a recording film 16 prepared as above. Next,in step (k-1), a pair of the above replica substrates 17 provided withthe foregoing recording film 16 are prepared, one of which is thenapplied with a reaction adhesive 18 by spin coating (30 μm thick) tofurnish a replica substrate 19 which is thus provided with the adhesiveformed on the recording film, and the rest of the pair is applied with aprimer 20 by spin coating (at 2000 rpm) to a thickness of 0.1 μm tofurnish another replica substrate 21 which is thus provided with theprimer formed on the recording film. In step (l-1), the above pair ofreplica substrates 19 and 21 are disposed in a hermetically sealed space22 such that the coated surfaces thereof face each other at a distanceof 5 mm. Then, the space 22 is substituted with nitrogen gas 23 for 60seconds in order to provide deoxygenation atmospheres. Then, in step(m-1) the pair of replica substrates 19 and 21 are moved for alignment,then bonded together. Further in step (n-1), by using ultravioletirradiation equipment 24, ultraviolet rays were irradiated onto theadhesives squeezed out of the peripheries exterior and interior of thedisc, thus accomplishing an optical disc according to the invention.

Preferred Embodiments 3 and 4

In this embodiments, adhesives of examples 3 and 4 in FIG. 9 were usedin the manufacture of a stamper which was prepared in the same manner asthe embodiments 1 and 2, then utilizing such a stamper an optical discwas produced according to a method of manufacturing thereof as shown inFIG. 5 from steps (g-2) through (m-2).

In step (g-2), the aforementioned stamper 7 was utilized as a mold, andin step (h-2) a UV curing resin 25 (with viscosity of 200 cp) wastrickled onto the recessed and raised surface of the stamper 7, then thetrickled UV curing resin 25 was pressed with a plastic plate 26 (outerdimension: 300 mm, internal dia.:35 mm, thickness: 1.1 mm) to uniformlyextend the adhesive to a film thickness of 80 micron m. After that, byutilizing the UV irradiation equipment 27, UV rays were irradiatedthrough the plastic plate on the UV curing resin 25 to cure (undercuring conditions: UV intensity; 100 mW/cm², for 30 s). In step (i-2),the UV cured resin 25 was severed from the stamper 7 at the interfacethereof to obtain a replica substrate 28 on the surface of which weretransferred the recessed and raised irregularities of grooves and pitsfrom the stamper 7. In step (j-2), on the surface of the replicasubstrate 28 obtained as above, there were formed a GeSbTe recordingfilm 29 (film thickness: 30 nm), an SbBi reflective film 30 (filmthickness: 20 nm), and an SiN protective film 31, successively bysputtering, thus providing a replica substrate 33 which was providedwith a lamination recording film 32. In step (k-2), a pair of the abovereplica substrates 33 provided with the lamination recording film wereprepared, the surface of one of the pair substrates 33 was applied witha reaction adhesive 18 by spin coating (to a film thickness of 30 μm) toprovide a replica substrate 34, and the surface of the other one of thepair substrates 33 was spin coated (rotation: 2000 rpm) with a primer 20on the recording film thereof to a film thickness of 0.1 μm to provide areplica substrate 35, respectively. In step (l-2), the above pair of thereplica substrates 34 and 35 were disposed at a distance of 5 mm in ahermetically sealed space 22 with the coated surfaces thereof facingeach other, and the space 22 thereof was evacuated to 20 mTorr in orderto attain a deoxygenation atmosphere. In step (m-2) the evacuated spacewas returned to the atmospheric pressure filled with nitrogen gas 23,then the pair of the replica substrates 34 and 35 disposed therein werebonded together to provide an optical disc according to the presentinvention.

Preferred Embodiments 5, 6

In this preferred embodiments of the invention, adhesives of examples 5and 6 in FIG. 9 were used in the manufacture of a stamper which wasprepared in the same manner as the embodiments 1 and 2, then utilizingsuch a stamper, optical discs were produced according to a method ofmanufacturing thereof as shown in FIG. 6 from steps (g-3) through (m-3).

In step (g-3), the stamper 7 described above was attached to a mold 8,then in step (h-3) a hot-melt polycarbonate resin 10 (molecular weight:approx. 15000) was injected into a space 9 (outer dia.: 300 mm, centerpore dia.: 35 mm, thickness: 1.2 mm) inside the mold, thus providing areplica substrate 11 (outer dia.:300 mm, center pore diam.: 35 mm,thickness: 1.2 mm) on the surface of which the irregularities of groovesand pits of the stamper were transferred as shown in step (i-3). Then,in step (j-3), on the surface of the above replica substrate 11 havingtransferred information patterns were formed a GeSbTe recording film 29(film thickness: 30 nm), an SbBi reflective film 30 (film thickness: 20nm) and an SiN protective film 31 (film thickness: 30 nm) successivelyby sputtering, thereby providing a replica substrate 36 provided with alamination recording film 32. In step (k-3), a pair of the above replicasubstrates 36 provided with the lamination recording film were prepared.On the surface of one of the pair of the substrates, reaction adhesive18 was spin coated to a thickness of 30 μm, thus providing a replicasubstrate 37 provided with the recording film and the adhesive appliedthereon. On the surface of the other one of the pair of the substrates36, a primer 20 was applied to a film thickness of 0.1 μm by the spincoating method (rotation: 2000 rpm), thereby providing a replicasubstrate 38 provided with the recording film and the primer coatedthereon. In step (l-3), the above pair of the replica substrates 37 and38 were disposed at a distance of 5 mm in the hermetically sealed space22 with the coated surfaces thereof facing each other, then the space 22was substituted with nitrogen gas 23 for 60 seconds to attain adeoxygenation atmosphere. In step (m-3), after moving horizontally thepair of the replica substrates 37 and 38 for alignment, they wereadhered together. Further, in step (n-3), adhesives squeezed out of theperipheral sides external and internal of the disc were exposed to UVrays from the ultraviolet irradiation equipment 24 under irradiationconditions: UV intensity of 30 mW/cm², duration of 10 seconds, therebyaccomplishing an optical disc according to the present invention.

Preferred Embodiment 7

In this preferred embodiments of the invention, an exemplary adhesive 7in FIG. 9 was used in the manufacture of a stamper which was prepared inthe same manner as the embodiments 1 and 2, then utilizing such astamper, optical discs were produced according to a method ofmanufacturing thereof as shown in FIG. 7 from steps (g-4) through (m-4).

In step (g-4), the aforementioned stamper 7 was utilized as a mold, andin step (h-4) a UV curing resin 25 (with viscosity of 200 cp) wastrickled onto the recessed and raised surface of the stamper 7, then thetrickled UV curing resin 25 was pressed with a plastic plate 26 (outerdimension: 300 mm, internal dia.:35 mm, thickness: 1.1 mm) to uniformlyextend to a film thickness of 80 μm. After that, by utilizing the UVirradiation equipment 27, UV rays were irradiated through the plasticplate on the UV curing resin 25 to cure (under curing conditions: UVintensity; 100 mW/cm², for 30 s). In step (i-4), the UV cured resin 25was severed from the stamper 7 at the interface thereof to obtain areplica substrate 28 on the surface of which were transferred therecessed and raised irregularities of grooves and pits from the stamper7. In step (j-4), on the surface of the replica substrate 28 obtained asabove, there were formed a SiN enhance film 12 (film thickness: 30 nm),a TbFeCo magnetic film 13 (film thickness: 30 nm), an AlN reflectivefilm 14 (film thickness: 30 nm) and an SiN protective film 15,successively by sputtering, thus providing a replica substrate 29 whichwas provided with a lamination recording film 16. In step (k-4), a pairof the above replica substrates 29 provided with the laminationrecording film were prepared, the surface of one of the pair substrates29 was applied with a reaction adhesive 18 by spin coating (to a filmthickness of 30 μm) to provide a replica substrate 40, and the surfaceof the other one of the pair substrates 29 was spin coated (rotation:2000 rpm) with a primer 20 on the recording film thereof to a filmthickness of 0.1 μm to provide a replica substrate 41, respectively. Instep (l-4), the above pair of the replica substrates 40 and 41 weredisposed at a distance of 5 mm in a hermetically sealed space 22 withthe coated surfaces thereof facing each other, and the space 22 thereofwas evacuated to 20 mTorr in order to attain a deoxygenation atmosphere.In step (m-4) the evacuated space was returned to the atmosphericpressure filled with nitrogen gas 23, then the pair of the replicasubstrates 40 and 41 disposed therein were bonded together to provide anoptical disc according to the present invention.

Comparative Examples 1 and 2

In this comparative examples of the invention, by utilizing adhesives ofcomparative examples 1 or 2 in FIG. 9, and according to the samemanufacturing method as for the preferred examples 1 and 2, opticaldiscs pursuant to the present invention were fabricated for comparison.

Comparative Examples 3 and 4

In this comparative examples of the invention, by utilizing adhesives ofcomparative examples 3 or 4 in FIG. 9, and according to the samemanufacturing method as for the preferred examples 3 and 4, opticaldiscs pursuant to the present invention were fabricated for comparison.

Comparative Examples 5 and 6

In this comparative examples of the invention, by utilizing adhesives ofcomparative example 5 in FIG. 9 and comparative example 6 in FIG. 10,and according to the same manufacturing method as for the preferredexamples 5 and 6, optical discs pursuant to the present invention werefabricated for comparison.

Comparative Examples 7 and 8

In this comparative examples of the invention, by utilizing adhesives ofcomparative examples 7 or 8 in FIG. 10, and according to the samemanufacturing method as for the preferred example 7, optical discspursuant to the present invention were fabricated for comparison.

Comparative Examples 9 and 10

In this comparative examples of the invention, by utilizing hot-meltadhesives of comparative examples 9 or 10 in FIG. 11, a pair of replicasubstrates provided with a recording film as shown in step (i-1) in FIG.4 explanatory of the preferred examples 1 and 2 were obtained. Then,after applying hot-melt adhesive on the surfaces of the recording filmsof the pair of the replica substrates by a hot-melt coater to athickness of 30 μm, the adhesive coated surfaces were disposed facingeach other and laminated under a load of 2 kg/cm² to provide an opticaldisc of the comparative example 9, and another pair of the same werelaminated under a load of 20 kg/cm² to provide an optical disc of thecomparative example 10, respectively.

Comparative Example 11

In this comparative example of the invention, by utilizing one-partanaerobic adhesive of example 11 in FIG. 11, a pair of replicasubstrates provided with a recording film as shown in step (i-1) in FIG.4 explanatory of the preferred embodiments 1 and 2 were prepared. Afterapplying the one-part anaerobic adhesive on the surface of the recordingfilm of one of the pair replica substrates by spin coating, the pair ofthe replica substrates were bonded and laminated under a reducedatmosphere of 20 mTorr to provide an optical disc according to thepresent invention.

Comparative Example 12

In this comparative example of the intention, by utilizing the two-partunmixture adhesive of comparative example 12 in FIG. 11, a pair ofreplica substrates provided with a recording film as shown in step (i-1)in FIG. 4 which is explanatory of the preferred embodiments 1 and 2 ofthe invention were prepared. Then, after applying type A agent of thetwo-part unmixture adhesive on the recording film surface of one of thepair of the replica substrates, and applying type B agent thereof on therecording film surface of the other one of the pair of the replicasubstrates by spin coating, the pair of the replica substrates werebonded and laminated under a reduced atmosphere of 20 mTorr to providean optical disc according to the present invention.

The aforementioned preferred examples 1 through 7 and comparativeexamples 1 through 12 of optical discs prepared by utilizing variousadhesives having different hardness according to the present inventionwere investigated as to (1) the instantaneous axial acceleration at roomtemperatures (about 25° C.) which corresponds to the degrees ofirregularity defects formed in the interface during bonding andlamination, (2) the skew angle at room temperatures (about 25° C.) whichchanges corresponds to the degrees of deformation, warps and peeling inthe optical disc, (3) the shear mass occurring between a pair of thesubstrates bonded together, after being left for one hour as heated to80° C., (4) the disc skew angle after being left for one hour as heatedto 80° C., and (5) the presence of defects such as irregularities, warpand peeling in the disc surfaces, detectable (through visual inspection)after bonding and lamination (at the time of manufacturing) and afterbeing left as heated (during operation or storage). The results areshown in FIGS. 12 and 13. Further, respective methods for measurementsof the aforementioned characteristics are described in the following.

(1) The instantaneous axial accelerations and (2) dynamic properties ofthe skew angles were measured with an optical disc dynamic propertymeasurement apparatus (laser wavelength: 780 nm, the number of measuringrotation: 2400 rpm, measurement position: φ290 mm²).

(3) The shear mass was measured from a displacement between the discsurfaces (film thickness: 30 μm, contact area: 6 cm²) when a shearingload of 500 g was applied.

(5) The detection of defects through visual inspection was conducted bymeans of the shadowgraph method whereby reflected light from an objectilluminated for inspection was projected to form a magnified image. Forinstance, when there exist irregularities, warps and deflection in theoptical discs, they are magnified on a projected image as shadows oflight or varied from normal scales.

From the results of FIGS. 12 and 13, relationships as shown in FIG. 8were obtained for the skew angles and the instantaneous axialaccelerations relative to the hardness of adhesives used in respectiveoptical discs. It is clearly understood from FIG. 8 that the skew anglesin the discs relative to the hardness of adhesives exceeding A30 fallwithin a limit of 5 mrad which is an object value, even for the examplesleft as heated to 80° C. Also, it is indicated clearly in FIG. 8 thatthe instantaneous axial accelerations in the optical discs relative tothe hardness of adhesives below A80 fall within a limit of 2 G which isan object value. The optical discs of the preferred examples 1 through 7of the invention, which were bonded and laminated with adhesives havingShore hardness between A30 and A80, satisfy the object values for theskew angles and the instantaneous axial accelerations concurrently. Onthe other hand, the optical discs provided as the comparative examplessatisfy only one of the attributes required as above. Further, thepresence of defects was checked for through visual inspection at thetime of manufacture of discs and after being left as heated, and it wasconfirmed that there occurred no defects in the preferred examples 1through 7 both at the time of manufacture and after being left asheated. In contrast, the optical discs of the comparative examples haveexhibited defects. For instance, the comparative examples 1 through 8,11 and 12 involved defects which occurred at the time of manufacturethereof, and in the comparative example 9 there occurred defects afterbeing left as heated, further in the comparative example 10 thereoccurred defects both at the time of manufacture and after being left asheated.

Further, with respect to the optical discs of the preferred examples 1through 7, a series of performance tests were conducted by recording andreproducing information at a disc rotation speed of 2400 rpm on arecording and reproduction apparatus (with a light source of 680 nmlaser beams, and a light head utilizing a condenser lens having thenumber of aperture of 0.55 and a focussing depth of approx. 2 micron m),without causing any degradation in recording and reproductionperformance.

As a result, it is verified that the optical discs bonded and laminatedwith the adhesives (having Shore hardness between A30 and A80 )according to the present invention are capable of providing an excellentoptical disc having an improved planar surface with less irregularitiesand deformation caused even under high temperatures environments,thereby providing a high precision performance thereof.

According to the present invention as set forth in detail heretofore, itis capable of implementing an optical disc and a method of manufacturingthe same, whereby deformation due to high speed access or high speedrotation, and warp and deflection or peeling due to aging during storageare substantially reduced, thereby realizing a high precision and highreliability optical disc.

We claim:
 1. An optical reproduction apparatus having an optical discand an optical head, said optical disc having a cross-sectionalstructure comprising a pair of transparent substrates each having atleast one layer of a recording film formed on a surface of informationpatterns thereof and the pair being bonded and laminated with anadhesive, wherein said optical disc is characterized by having aninstantaneous axial acceleration <2G measured at room temperature, askew angle <5 mrad measured at room temperature and a skew angle <5 mradmeasured at room temperature after being left for one hour as heated to80° C.
 2. The optical reproduction apparatus according to claim 1,wherein said adhesive is characterized by being a reaction adhesive. 3.The optical reproduction apparatus according to claim 2, wherein saidreaction adhesive is characterized by consisting essentially of anaccelerator primer and a one-part anaerobic adhesive.
 4. The opticalreproduction apparatus according to claim 3, wherein said one-partanaerobic adhesive is characterized by being a one-part anaerobic UVcuring adhesive.
 5. The optical reproduction apparatus according toclaim 3, wherein said accelerator primer is characterized by having aviscosity of between 1 and 100 cp.
 6. The optical reproduction apparatusaccording to claim 3, wherein said one-part anaerobic adhesive comprisesacrylate monomer as a main component, a curing agent, an accelerator anda preservation stabilizer.
 7. The optical reproduction apparatusaccording to claim 6, wherein said acrylate monomer is characterized bybeing at least one of a one-functional acrylic monomer and amultifunctional acrylic monomer.
 8. An optical reproduction apparatushaving an optical disc and an optical head, said optical disc having across-sectional structure comprising a pair of transparent substrateseach having at least one layer of a recording film formed on a surfaceof information patterns thereof and the pair being bonded and laminatedwith an adhesive, wherein said optical disc is characterized by havingan instantaneous axial acceleration <2 g measured at room temperature, askew angle <5 mrad measured at room temperature and a shear mass <20 μmmeasured at room temperature after being left for one hour as heated to80° C.
 9. The optical reproduction apparatus according to claim 8,wherein said adhesive is characterized by being a reaction adhesive. 10.The optical reproduction apparatus according to claim 9, wherein saidreaction adhesive is characterized by consisting essentially of anaccelerator primer and a one-part anaerobic adhesive.
 11. The opticalreproduction apparatus according to claim 10, wherein said one-partanaerobic adhesive is characterized by being a one-part anaerobic UVcuring adhesive.
 12. The optical reproduction apparatus according toclaim 10, wherein said accelerator primer is characterized by having aviscosity of between 1 and 100 cp.
 13. The optical reproductionapparatus according to claim 10, wherein said one-part anaerobicadhesive comprises acrylate monomer as a main component, a curing agent,an accelerator and a preservation stabilizer.
 14. The opticalreproduction apparatus according to claim 13, wherein said acrylatemonomer is characterized by being at least one of a one-functionalacrylic monomer and a multifunctional acrylic monomer.
 15. An opticalreproduction apparatus having an optical disc and an optical head, saidoptical disc having a cross-sectional structure comprising a pair oftransparent substrates each having at least one layer of a recordingfilm formed on a surface of information patterns thereof and the pairbeing bonded and laminated with an adhesive, wherein said adhesive ischaracterized by being a reaction adhesive having a hardness after curebetween A 30 and A 80 in Shore hardness.
 16. The optical reproductionapparatus according to claim 15, wherein said reaction adhesive ischaracterized by consisting essentially of an accelerator primer and aone-part anaerobic adhesive.
 17. The optical reproduction apparatusaccording to claim 16, wherein said one-part anaerobic adhesive ischaracterized by being a one-part anaerobic UV curing adhesive.
 18. Theoptical reproduction apparatus according to claim 16, wherein saidaccelerator primer is characterized by having a viscosity of between 1and 100 cp.
 19. The optical reproduction apparatus according to claim16; wherein said one-part anaerobic adhesive comprises acrylate monomeras a main component, a curing agent, an accelerator and a preservationstabilizer.
 20. The optical reproduction apparatus according to claim19, wherein said acrylate monomer is characterized by being at least oneof a one-functional acrylic monomer and a multifunctional acrylicmonomer.
 21. An optical reproduction apparatus having an optical discand an optical head, said optical disc comprising a pair of replicasubstrates, each of which comprises a transparent substrate having aninformation surface with information patterns formed in said informationsurface and at least one recording film overlying said informationsurface of the transparent substrate; and an adhesive layer of areaction adhesive overlying said recording films of the pair of replicasubstrates, thereby bonding the pair of replica substrates to eachother; wherein said adhesive is characterized by having a Shore hardnessafter cure between A 30 and A
 80. 22. The optical reproduction apparatusaccording to claim 21, wherein said reaction adhesive is characterizedby consisting essentially of an accelerator primer and a one-partanaerobic adhesive.
 23. The optical reproduction apparatus according toclaim 22, wherein said one-part anaerobic adhesive is characterized bybeing a one-part anaerobic UV curing adhesive.
 24. The opticalreproduction, apparatus according to claim 22, wherein said acceleratorprimer is characterized by having a viscosity of between 1 and 100 cp.25. The optical reproduction apparatus according to claim 22, whereinsaid one-part anaerobic adhesive comprises acrylate monomer as a maincomponent, a curing agent, an accelerator and a preservation stabilizer.26. The optical reproduction apparatus according to claim 25, whereinsaid acrylate monomer is characterized by being at least one of aone-functional acrylic monomer and a multifunctional acrylic monomer.